Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$84.66	5.182%	$89.0471	$89.05	$89.05	$89.00
Purchase #2	$34.33	8.531%	$37.2587	$37.26	$37.25	$37.30
Purchase #3	$168.41	6.292%	$179.0064	$179.01	$179.00	$179.00
Purchase #4	$220.35	5.239%	$231.8941	$231.89	$231.90	$231.90
Purchase #5	$158.75	13.453%	$180.1066	$180.11	$180.10	$180.10
Purchase #6	$40.52	5.353%	$42.689	$42.69	$42.70	$42.70
Purchase #7	$102.45	7.795%	$110.436	$110.44	$110.45	$110.40
7 purchase totals =	$809.47		$870.4379	$870.45	$870.45	$870.40